Results of a Rice University laboratory study suggests that using foam may maximize enhanced oil recovery (EOR). In the experiments, foam pumped into an experimental rig that mimicked the flow paths deep underground proved better at removing oil from formations with low permeability than common techniques involving water, gas, surfactants or combinations of the three. The open-access paper led by Rice scientists Sibani Lisa Biswal and George Hirasaki is published in the RSC journal Lab on a Chip.

Oil resides in formations of rock and sand in small cracks and crevices that have proved devilishly difficult to tap. Drillers pump various substances downhole to loosen and either push or carry oil to the surface.

Biswal’s lab created microfluidic models of formations to see how well foam stacks up against other materials in removing as much oil as possible. The formations are not much bigger than a postage stamp and include wide channels, large cracks and small cracks. By pushing various fluids, including foam, into test formations, the researchers can visualize the ways by which foam is able to remove oil from hard-to-reach places. They can also measure the fluid’s pressure gradient to see how it changes as it navigates the landscape.

Foam dislodged all but 25.1% of oil from low-permeability regions after four minutes of pushing it through a test rig, versus 53% for water and gas and 98.3% for water flooding; this demonstrated efficient use of injected fluid with foam to recover oil.

The less-viscous fluids appear to displace oil in high-permeability regions while blowing right by the smaller cracks; foam offers mobility control, which means a higher resistance to flow near large pores.

The foam’s lamellae (the borders between individual bubbles) add extra resistance to the flow. Water and gas don’t have that ability, so it’s easy for them to find paths of least resistance and move straight through. Because foam acts like a more viscous fluid, it’s better able to plug high-permeable regions and penetrate into less-permeable regions.

—Sibani Lisa Biswal

Charles Conn, a Rice graduate student and lead author of the paper, said foam tends to dry out as it progresses through the model. Drying has two effects: It slows the progress of the foam even further and allows surfactant from the lamellae to drain into low-permeability zones, where it forces oil out. Foam may also cut the sheer amount of material that may have to be sent downhole.

One of the challenges will always be to get the foam to the underground formation intact.

It’s nice to know that foam can do these things, but if you can’t generate foam in the reservoir, then it’s not going to be useful. If you lose the foam, it collapses into slugs of gas and liquid. You really want foam that can regenerate as it moves through the pores.

—Charles Conn

The lab plans to test foam on core samples that more closely mimic the environment underground, Biswal said.

Kun Ma, a Rice alumnus, co-authored the paper. The Department of Energy, the Abu Dhabi National Oil Co., the Abu Dhabi Oil R&D Sub-Committee, the Abu Dhabi Co. for Onshore Oil Operations, the Zakum Development Co., the Abu Dhabi Marine Operating Co. and the Petroleum Institute of the United Arab Emirates supported the research.